Electroencephalography signals are often analysed and reviewed in order to make sense of, and/or to condense the copious amount of data collected from the brain of a subject under study. Techniques include many frequency-based derivatives such as the fast Fourier transform, counts of zero crossings, spectral analysis, spectral edge, intensity, and the like.
The applicant is the assignee of patent applications and patents such as U.S. Pat. No. 6,406,427 relating to a brain monitoring device first intended for use with premature near-term human infants many of whom suffer brain trauma near the time of delivery. Monitoring can lead to appropriate treatments and to a better indication of outcome.
However, in a hospital's Intensive Care Unit (ICU), it is also necessary to be able to monitor brain seizures in term infants through to adults. In this environment, patients are often paralyzed or unconscious and seizures are silent and can not currently be reliably observed or monitored. Often, only significant/severe seizures need be detected but detection needs to be carried out with a very high degree of reliability in order to be able to assist busy non-expert staff in the ICU.
Further applications of the device include the monitoring of anaesthesia and brain function during and after procedures such as open-heart surgery in which micro-emboli lodging within end-arteries are not uncommon.
The pathology of brain damage includes a primary and a secondary response at least part of which is endogenous damage, as exhibited by neurones. Sometimes seizures, which may lack correlated clinical signs perhaps because of administered drugs, form part of the response pattern. A seizure involves the synchronous firing of a large number of neurones, which is abnormal. A resulting waveform may comprise a distinctive regular series of waves ranging from very sharp “spikes” to “sine-like waves” originating from firing by many neurones in unison within the field under study, although in a pre-term infant, especially if already under treatment, or if the damage site is small or localised, the waveforms may be relatively small and difficult to recognise.
One reason to seek the recognition of seizure waveforms is that if they can then be inhibited or suppressed by drugs or other treatment the outcome for the patient is usually improved.
There is a need for an automatic form of seizure detection by instrumental means (usually operating within a brain monitoring device), so that continuous, reliable, and immediate reporting of the onset or existence of a seizure is provided. It would be an advantage to be able to provide a very reliable severe seizure monitor suitable for use in an Intensive Care Unit of a hospital.
WO02071936A and the article entitled “A real-time algorithm for the qualification of blood pressure waveforms” published in IEEE Transactions on Biomedical Engineering Vol. 49, No. 7. July 2002 disclose a real time algorithm for the quantification of biological oscillatory signals such as arterial blood pressure. The algorithm analyses the original signal by determining certain parameters so that false peaks (which are typical of arterial blood pressure signals) can be removed to accurately quantify heartbeats.
It is therefore an object of this invention to provide real-time seizure detection by instrumental means (that is, without human analysis) which will go at least some way towards meeting the above requirements or which will at least to provide the industry with a useful choice.